1. Field of the Invention
The present invention relates to a fuel cap for a fuel tank for a motor vehicle.
2. Description of the Related Art
Although a fuel cap for a fuel tank for a motor vehicle is a simple part, it is important to maintain the high air-tightness function of the cap with respect to an oil filler port in a stage in which the fuel cap is turned in the closing direction with respect to an oil filler port and thereby completely finished the securing operation. This stage is hereinafter referred to as a “securing-finished” stage. The improvement of the operability of the fuel cap turning operation from a stage in which the fuel cap is inserted into the fuel filler port and started being turned in the closing direction (, and this stage is hereinafter refereed to as a “securing-started” stage,) to the securing-finished stage, i.e. the simplification of the fuel cap opening and closing operations and, especially, the reduction of the torque needed to turn the fuel cap in the closing direction are demanded.
The conventional fuel caps produced with the attention paid to the improvement of the operability thereof can include the fuel caps disclosed in, for example, Japanese Patent No. 2712115 and JP-T-09-512770. The fuel cap disclosed in Japanese Patent No. 2712115 compresses a seal ring owing to an operation of a cam mechanism urged downward by a spring in a final stage of an operation for securing the fuel cap to the oil filler port, and thereby attains the air-tightness of the fuel cap. The quantity of turn of the fuel cap needed to operate the cam mechanism may be small, and a turning operation for compressing the seal ring is not necessary. Therefore, it can be said that the operability of the fuel cap is improved.
The fuel cap disclosed in JP-T-09-512770 is also formed identically with that disclosed in Japanese Patent No. 2712115. The fuel cap disclosed in this patent is tightened on the oil filler port by a small quantity of turn (⅛ turn) thereof. However, when the fuel cap receives an external force, such as an impact force, there is a fear of coming off of the fuel cap from the oil filler port. In order to eliminate this inconvenience, a structure for turning idly a handle of the fuel cap engaged with the oil filler cap is added. Although an excessive turning operation corresponding to the idle turn of the handle comes to be needed to remove the fuel cap from the oil filler port but, in spite of this, a fuel cap turning operation of as large as one turn is not needed. Therefore, it can be said that the operability of the fuel cap is still excellent.
In the fuel caps disclosed in Japanese Patent No. 2712115 and JP-T-09-512770, the air-tightness thereof is attained by vertically compressing the seal ring in contact with an end of the oil filler port. Reversely speaking, it means that the air-tightness of the fuel cap cannot be secured unless the seal ring is uniformly in contact with the end of the oil filler port. Therefore, a structure capable of securing the air-tightness of the fuel cap even when the fuel cap is in a twisted positional relation with respect to the oil filler port is necessarily demanded. Concerning this point, in the fuel cap disclosed in JP-A-2002-293356, inclination preventing ribs are provided so that the twisting of the fuel cap itself does not occur. Thus, a decrease in the air-tightness of the fuel cap ascribed to the ununiform compression of the seal ring is prevented.